sedimentary

Likely weathered flint or chert nodule

Microcrystalline quartz (SiO₂), commonly with chalcedony and impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; gray-brown to tan, dull-to-waxy luster, opaque, very fine-grained and conchoidally fracturing. The irregular shape and dark, glassy fracture surfaces are consistent with flint/chert, though the image alone cannot confirm the identification.

Identified September 13, 2026More sedimentary →

Explore Likely weathered flint or chert nodule in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone or chalk, generally during burial and diagenesis; its age depends on the host sediment, commonly Paleozoic to Cretaceous. Weathering can produce a pale cortex and rusty iron-oxide staining.

Uses & applications

Used historically for sharp tools and fire-starting, and today mainly as a lapidary, teaching, or collector specimen; crushed chert can serve as aggregate. It has little gem value unless unusually patterned or colorfully banded.

Geological facts

Flint is a variety of chert, typically dark and associated with chalk, while chert is the broader term. Freshly broken surfaces may be sharp enough to cut skin.

Field identification & locations

Common in limestone/chalk terrains, including parts of Europe and North America; test cautiously for a glassy conchoidal fracture and inability to scratch it with a steel nail. A streak, acid, and microscopic examination help distinguish it from slag or other siliceous rocks.